野付崎における分岐砂嘴の発達

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Notsukezaki, well known as the typical compound recurved spit in Japan, develops over 20km in length toward SE from Shibetsu located in the middle of the east coast of Hokkaido. The writer tried to clarify the formation and the development of Notsukezaki, for that purpose, the coastal and submarine topography, recent deposits of the coast, winds speed and direction at Notskezaki are surveyed.Waves from the northeast are undoubtedly the active force, judging from the submarine topography and the fetch. Fig. 4 shows that the waves from NE causing wave erosion at the northern coast of Notsukezaki may permit to derive marine deposition southward. In fact, Fig. 5 proves that the northern coast is retreating and furnishing an abundant débris, besides, the materials of the cliff formation are easily eroded. Therefore, the longshore drifting caused by the predominant NW winds could carry an excessive amount of sand and gravel southward and produced the spit. Notsukezaki has been formed since post-glacial without any existing nucleus along the main direction depending upon the longshore current from NW to SE and the wave agency from NE.The beach ridges which built each of compound spit shows uniform height (Fig. 3). The fact expresses the level of beach ridges in terms of past sea level as shown in Fig. 6. The result can be correlated with Fairbridge (1961) favourably and the development of Notsukezaki associated with the fluctuation of sea level is schematically shown in Fig. 7.

野付崎における分岐砂嘴の発達

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